When causing a legged mobile robot, such as a bipedal mobile robot, to perform an operation of, for example, moving a certain object by pushing, the robot is subjected not only to a floor reaction force from a floor with which a distal portion of a leg body thereof is in contact but also to a reaction force from the object. The reaction force received by the robot from the object as described above will be referred to as an object reaction force in the present description.
As a technology for generating a gait of a robot in a state wherein an object reaction force is acting on a legged mobile robot, or for carrying out motion control, there has been known a technology disclosed in, for example, Japanese Patent Application Laid-Open Publication No. H10-230485 by the inventor of the present application (hereinafter referred to as Patent Document 1). According to the technology, a desired gait is generated such that a dynamic balance condition in which a component (horizontal component), excluding a vertical component, of a moment produced about a desired ZMP (a desired floor reaction force central point) by a resultant force of an inertial force produced due to a motion of a robot and the gravity and an object reaction force acting on the robot is zero (a floor reaction force acting on the desired floor reaction force central point and the aforesaid resultant force are balanced with each other) is satisfied, and the motions of the robot are controlled so that the desired gait is followed. Furthermore, according to the technology, even if an external force acting on the robot turns into an unexpected external force (even if a difference between a desired external force and an actual external force increases to a certain extent), a desired gait of the robot is adjusted such that a position of the center of gravity of the robot is balanced to a position of the center of gravity that makes it possible to maintain the dynamic balance of the robot.
Further, as a technology for simulating the behaviors of a bipedal mobile robot (humanoid robot), there has been known a technology disclosed in Scholarly Journal of the Robotics Society of Japan/Vol. 19/No. 1, pp. 28˜36, 2001/“Virtual Robot Platform” (hereinafter referred to as Non-Patent Document 1).
Meanwhile, when generating a desired gait of a robot for performing an operation of moving an object, generally, environmental conditions (the configuration of a floor, a frictional force condition, etc.) for moving the object are assumed, and then the basic parameters for generating a gait that define, for example, the trajectory of an object reaction force (a time series pattern), the motion trajectory of the object (the time series pattern of the movement position/posture of the object), and the motion trajectory of a distal portion of each leg body of the robot are determined on the basis of a plan for moving the object (such as a plan that specifies the timing and the method for moving the object). Then, by using the determined parameters, a desired gait of the robot is generated such that a dynamic restrictive condition (e.g., a condition that a ZMP satisfying the aforesaid dynamic balance condition lies within a ground contact surface of the robot) is satisfied under the aforesaid assumed environmental condition.
In this case, if the moving plan or the parameters for generating a gait are inappropriate, then a desired gait that fails to satisfy a geometric restrictive condition, such as the one in which the body of the robot does not bump against an object or in which an arm body of the robot to be engaged with the object does not exceed a movable range, may be inconveniently generated.
Hence, a solution is conceivable in which, for example, a desired gait is generated while simulating behaviors of a robot thereby to check whether a geometric restrictive condition is satisfied by applying the technology shown in the aforesaid Non-Patent Document 1 to the technology shown in the aforesaid Patent Document 1.
However, the technology shown in the aforesaid Non-Patent Document 1 is adapted to simulate (predict) a behavior of a robot on the assumption of a certain environmental condition, so that if an actual environmental condition differs from an assumed environmental condition (this situation frequently occurs), then a situation in which a generated desired gait actually fails to satisfy the aforesaid geometric restrictive condition frequently takes place.
The present invention has been made in view of the background described above, and it is an object of the invention to provide a gait generator of a legged mobile robot that is capable of generating a desired gait that makes it possible to satisfy a predetermined geometric restrictive condition related to the interference or the like between the robot and an object by reflecting an actual environmental condition in real time while controlling a motion of the robot.